This invention relates to a holder used at the time when a sealing member is hermetically sealed in a glass article, specifically, squeezed into a softened glass article. More specifically, it relates to a holder suitable for the hermetical sealing of panel pins in cathode ray tubes.
The hermetic sealing of sealing members being constituted of various sealing alloys to glass articles is carried out by planting the members in thermally softened portions of the glass articles, and at this time, a holder is used to squeeze the members into the glass articles.
For example, in a manufacturing process for the cathode ray tubes, there is a step of hermetically sealing by planting the panel pins for supporting a shadow mask at four positions on the inner wall of the edge portion of a panel face. One cycle of this step is usually composed of softening a panel glass by heating the panel face in the atmosphere, and planting the panel pins each having a predetermined size in the softened portions of the panel glass in a certain period of time by the use of the holder.
Such a conventional technique is disclosed in, for example, Japanese Patent Publication No. 24291/1973 (which corresponds to U.S. Pat. Nos. 3,441,706 and 3,589,001). In this technical concept, the holder made from aluminum oxide is described.
In general, the used panel pin is made from a material such as a 42% Ni-6% Cr-Fe alloy, and the holder is manufactured from a sintered alumina.
However, such an alumina holder has the following problems, and its lifetime is very short, with the result that the hermetic sealing step of the panel pins cannot be operated continuously for a long time.
That is, the above mentioned problems of the conventional holder are as follows: (1) since the hermetic sealing operation is carried out in the atmosphere, the surface of the panel pin will be oxidized, and the formed oxide (mainly chromium oxide) will meltingly adhere to the portion of the holder brought into contact with the panel pin and/or a vaporized substance from the oxide will deposit on the above portion of the holder, which fact will prevent the panel pins from being planted in accordance with a severe design criterion. Further, (2) the conventional alumina holder has a wettability to the oxide film of the panel pin and the panel glass at a high temperature, and thus the oxide film of the panel pin and the melted panel glass tend to adhere to the tip portion of the holder at hermetic sealing operation. Furthermore, (3) when the panel pin is planted, a great frictional force will occur between the head portion of the panel pin and the tip contact portion of the holder, and the friction of these portions will make progress with time, so that a mounting accuracy will finally deviate from the design criterion. Moreover, (4) in the hermetic sealing operation, a step of heating up to a temperature of several hundred to about 1,100.degree. C. and a subsequent step of being allowed to cool are repeated in one cycle of 30 to 60 seconds, and hence it is important that the holder is excellent in thermal shock resistance in addition to heat resistance, and that its wettability is small. In view of these points, the conventional alumina holder is not always satisfactory.
For these reasons, there is strongly desired an improvement in the holder made from a novel material which enables a lifetime to be prolonged and the panel pins to be hermetically sealed continuously for a long time.